For further information, see Chapter 4: Inland water.
River pollution often arises from upstream development and land use. However, it has particular impacts on the environment where it enters estuaries and the nearshore coastal environment. Some of the most significant of these estuaries and coastal lagoons are near our major cities (Sydney, Melbourne, Brisbane, Adelaide, Perth) or significant environmental assets (the Great Barrier Reef).
The land is a major source of coastal and marine pollution. Considerable progress has been made in addressing point-source pollution, although some problems still arise from these sources. Current diffuse pollution to catchments often results from historical land clearing and land-use changes. Urban stormwater is a major non–point source. Although extensive land clearing for agriculture has been considerably reduced in Australia, the legacy of sedimentation and salinisation of rivers continues. The millennium drought (lasting from 2000 to 2010 throughout southern Australia, but starting in 1997 in some areas) slowed some of these degrading processes in places, but it is likely that subsequent flooding will bring these issues back to the fore among environmental concerns.
Chapter 4: Inland water gives examples of major short-term increases in sedimentation after bushfires in south-eastern Australia (due to reduced vegetation cover and exposure of soil) and major longer term (25–30 years post-fire) reductions in water yield (due to regrowth of vegetation).
Most Australians live in metropolitan areas, most of which are located on the coast. Although many of these cities draw water from inland areas, pressure is increasing for them to be able to replace or supplement these inputs by collecting the water that falls as rain in their metropolitan areas and/or by desalinating sea water, as a hedge against climate change. This would reduce further pressure on local freshwater resources. However, it entails a potential risk to coastal waters if salt is disposed of into these waters, and will increase the overall energy use in our cities.
The amount of desalination undertaken by Australian cities increased sharply during 2005–10, largely in response to drought, climate uncertainty, population increase and a new understanding of the need to provide water flows to the environment. Desalination plants were commissioned in Sydney and at Tugun in south-east Queensland in 2010; others are under construction in Melbourne (completion 2011), Perth (completion 2011) and Adelaide (completion 2013). However, desalination is not a universal strategy, as many local governments have sought to manage demand for water and improve water saving at municipal and household levels, often avoiding the need for major new water infrastructure.
Development of groundwater resources to meet growing demands at the coast can put local aquifers at risk of seawater intrusion. Before development, groundwater gradients are naturally towards the sea and maintain an interface between fresh and salt water. If aquifers are exploited too heavily, this gradient can reverse and draw sea water into previously fresh aquifers. Rising sea levels also have the potential to reverse this gradient.
A number of locations around Australia have already been identified where seawater intrusion is a concern, including coastal locations in Queensland (Lower Burdekin, Bribie Island and the Pioneer Valley), South Australia (Eyre Peninsula, Port McDonnell and metropolitan Adelaide), Victoria (Port Phillip, Westernport and Werribee) and Western Australia (Swan Coastal Plain, Carnarvon, Esperance, Cottesloe and Cape Range).
Coastal development leading to increased groundwater use, potentially exacerbated by sea level rise, poses a risk to fresh groundwater resources and the people and natural environments they support.
Coastal environments and the species that inhabit them are particularly vulnerable to the effects of drought, because the impacts of drought are exacerbated by withdrawal (abstraction) of water for human use along rivers before they reach the coast. Impacts on waterbird and shorebird populations due to abstractions and extended drought were evident by 2008. The annual survey of waterbird communities at the Living Murray icon sites found a 48% decrease in bird numbers from the previous year. No waterbird breeding was recorded at the Lower Lakes, Coorong and Murray mouth, and only minimal breeding of white ibis and black swans was recorded at Chowilla Floodplain and Lindsay–Wallpolla islands. The decline of inland wetlands was identified as a significant contributor to the drastic decline in shorebirds (73% and 81% declines for migratory and resident shorebirds, respectively) between 1983 and 2006.
Management of coastal waters has improved greatly in Australia during the past decade, including some high-profile programs to ensure river and estuary health in metropolitan areas (e.g. Hobart and Brisbane). These programs have developed and tested cost-effective approaches to monitoring, modelling, reporting, innovation, communication, strategic interventions and effective partnerships between researchers and managers. Another successful approach to the management of coastal waters is described in Box 11.1.